Three-dimensional form measurement device

Abstract

A three-dimensional form measurement device includes: an interference fringe projector that scans an interference fringe and projects one of a plurality of interference fringe patterns; an imaging device that images the subject of measurement onto which the interference fringe is projected and generates a plurality of interference fringe images corresponding to at least three different interference fringe patterns in each of a plurality of imaging conditions; and a controller that selects, for each pixel, which imaging condition should be used to compute a phase distribution image of the subject of measurement, and computes a phase of each pixel in the phase distribution image based on the pixel values in the plurality of interference fringe images corresponding to the imaging condition selected for each pixel.

What is claimed is: 
     
       1. A three-dimensional form measurement device comprising:
 an interference fringe projector that scans an interference fringe and projects N interference fringe patterns that differ in dark and bright positions in the interference fringe onto a subject of measurement, where N is a natural number larger than 2; 
 an imaging device that includes an image sensor and that images the subject of measurement onto which the interference fringe is projected under M different imaging conditions, and generates N*M interference fringe images corresponding to the N different interference fringe patterns in each of the M different imaging conditions, where M is a natural number larger than 1; and 
 a controller that:
 selects, for each pixel in a phase distribution image of the subject of measurement which is to be computed, one of the M different imaging conditions; and 
 computes a phase of each pixel in the phase distribution image based on pixel values in N of the N*M interference fringe images imaged under the one of the M different imaging conditions selected for each pixel so as to compute three-dimensional form data of the subject of measurement. 
 
 
     
     
       2. The three-dimensional form measurement device according to  claim 1 , wherein the M different imaging conditions differ in respect of at least one of an exposure time of the image sensor provided in the imaging device, a light amount incident on the image sensor, a gain of an image signal of the image sensor, a position of the interference fringe projector with respect to the imaging device, and a light intensity of the interference fringe projected from the interference fringe projector. 
     
     
       3. The three-dimensional form measurement device according to  claim 1 , wherein the controller computes the phase of each pixel in the phase distribution image based on the pixel values in the plurality of N of the N*M interference fringe images corresponding to the N different interference fringe patterns imaged under the same imaging condition and based on an amount of phase shift between the N different interference fringe patterns. 
     
     
       4. The three-dimensional form measurement device according to  claim 1 , wherein the controller selects said one of the M different imaging conditions for each pixel in the phase distribution image based on the pixel values in the N*M interference fringe images and a reference value determined in accordance with a number of shades of the image sensor provided in the imaging device. 
     
     
       5. The three-dimensional form measurement device according to  claim 4 , wherein the controller compares the pixel values in the N*M interference fringe images between the M different imaging conditions and selects, as said one of the M different imaging conditions for each pixel, an imaging condition in which the pixel value has a maximum value on a condition that the pixel value is equal to or smaller than the reference value. 
     
     
       6. The three-dimensional form measurement device according to  claim 1 , wherein the controller computes for each pixel an amplitude of variation between the pixel values in the N*M interference fringe images caused by scanning the interference fringe, based on the pixel values in N of the N*M the interference fringe images corresponding to the N different interference fringe patterns captured in the same imaging condition and on an amount of phase shift between the N different interference fringe patterns, and selects said one of the M different imaging conditions for each pixel in the phase distribution image based on the amplitude of variation between the pixel values computed. 
     
     
       7. The three-dimensional form measurement device according to  claim 6 , wherein the controller compares the pixel values in the N*M interference fringe images between the M different imaging conditions and selects, as said one of the M different imaging conditions for each pixel, an imaging condition in which the amplitude of variation between the pixel values computed has a maximum value on a condition that the pixel value is equal to or smaller than a reference value determined in accordance with the number of shades of the image sensor provided in the imaging device. 
     
     
       8. The three-dimensional form measurement device according to  claim 1 , wherein the controller computes, for each of the M different imaging conditions, a reliability distribution indicating reliability of the pixel values in the N of the N*M interference fringe images imaged under the same imaging condition, and selects said one of the M different imaging conditions for each pixel by comparing reliability distributions computed. 
     
     
       9. The three-dimensional form measurement device according to  claim 1 , wherein the imaging device includes the image sensor and an imaging optical system including a lens for forming an image of the subject of measurement onto which the interference fringe is projected in the image sensor,
 wherein a wavelength λ of light projected by the interference fringe projector, a pitch p of a unit formed by one or a plurality of pixels of the image sensor and corresponding to one pixel in the interference fringe image, a minimum F-number of the imaging optical system at the wavelength λ, and a lateral magnification M of the imaging device at the wavelength λ meet the following expression (1)
   1.22(1+ M )λ F ≤√{square root over (2)} p   (1).
 
 
 
     
     
       10. The three-dimensional form measurement device according to  claim 1 , wherein the interference fringe projector includes:
 a light source that radiates coherent light; 
 a branching filter that causes a light beam radiated from the light source to branch; and 
 a phase modulator that changes a phase of at least one of light beams output by the branching filter. 
 
     
     
       11. The three-dimensional form measurement device according to  claim 10 , wherein the interference fringe projector further includes a light source controller that maintains a wavelength of the light beam radiated from the light source to be constant and a light modulator that modulates a light amount of the light beam radiated from the light source. 
     
     
       12. The three-dimensional form measurement device according to  claim 1 , wherein the imaging device captures the N*M interference fringe images corresponding to the M different imaging conditions in a time divided manner. 
     
     
       13. The three-dimensional form measurement device according to  claim 1 , wherein the imaging device includes a plurality of image sensors and a light path branching unit that includes a prism and that causes an imaging light from the subject of measurement to branch toward each of the plurality of sensors and configures imaging conditions of the plurality of image sensors to be different. 
     
     
       14. The three-dimensional form measurement device according to  claim 13 , wherein the imaging device simultaneously captures interference fringe images in different imaging conditions. 
     
     
       15. The three-dimensional form measurement device according to  claim 1 , wherein:
 the image sensor includes a plurality of pixels arranged in a two-dimensional array, and each of the plurality of pixels is configured such that at least one of an exposure time of a given pixel, a light amount incident on the given pixel, and a gain of an output signal of the given pixel differs from the exposure time, the light amount, or the gain of another of the plurality of pixels. 
 
     
     
       16. The three-dimensional form measurement device according to  claim 1 , wherein the interference fringe projector includes a first interference fringe projector that projects an interference fringe pattern onto the subject of measurement from a first position and a second interference fringe projector that projects an interference fringe pattern onto the subject of measurement from a second position different from the first position. 
     
     
       17. The three-dimensional form measurement device according to  claim 16 , wherein:
 the controller switches between interference fringe projection by the first interference fringe projector and interference fringe projection by the second interference fringe projector, and 
 the imaging device captures an interference fringe image based on the interference fringe projection by the first interference fringe projector and an interference fringe image based on the interference fringe projection by the second interference fringe projector in a time divided manner.